[JAVA][RestTemplate]Query parameter is not URL encoded

Created by: simingweng

Description

If an API accept query parameter and parameter contains unsafe symbol, such as "&" sign, in the RestTemplate-based Java client, it is not encoded. When the request is sent as it is to the server side, it prevents the server from parsing the parameter properly.

openapi-generator version

3.0.0

OpenAPI declaration file content or url

https://github.com/OpenAPITools/openapi-generator/blob/v3.0.0/modules/openapi-generator/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml

Command line used for generation

https://github.com/OpenAPITools/openapi-generator/blob/v3.0.0/bin/java-petstore-resttemplate.sh

Steps to reproduce

the line of code in question is at https://github.com/OpenAPITools/openapi-generator/blob/9c82520637b9cd4415046e78ddb13dec84e89509/samples/client/petstore/java/resttemplate/src/main/java/org/openapitools/client/ApiClient.java#L518

the parameter string are put into UriComponentsBuilder as it is

Suggest a fix/enhancement

It seems other flavour of Java clients, such as "okhttp-gson", is doing "escaping" while building the request, at https://github.com/OpenAPITools/openapi-generator/blob/9c82520637b9cd4415046e78ddb13dec84e89509/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/ApiClient.java#L1037

we need to introduce this sanitisation in RestTemplate-based client